SWEETENED CONDENSED MILK DEFECTS 211 



less those violent gas-producing butyric acid bacteria and yeast 

 cells, which thrive in sweetened condensed milk containing 40 

 per cent, sucrose, the product would be objectionable from the 

 consumer's point of view. The logical avoidance of "swell heads" 

 as the result of these undesirable germs, therefore, must ever lie 

 in prevention, rather than cure. The sanitary standard of pro- 

 duction on the farm and of the process in the factory must be 

 raised to and maintained on a level where the milk is protected 

 from contamination with these micro-organisms. 



The writer 1 has isolated yeast from fermented sweetened 

 condensed milk that produced vigorous gas formation in media 

 containing as high as 85 per cent, sucrose (600 grams sucrose in 

 100 cc. whey bouillon). 



Effect of Too Thin Condensed Milk. Condensed milk that 

 is too thin is, also, prone to start fermenting, since it is deficient 

 in the chief preserving agents, i. e., density and per cent, of 

 sucrose. It is not safe to put goods on the market, with a ratio 

 of concentration much less than 2.5:1. 



Effect of Excessively Low Temperatures. The cans of 

 sweetened condensed milk may also bulge in the case of cans 

 with non-hermetical seals, exposed successively to excessive cold 

 and to room temperature. In this case, the condensed milk is 

 entirely normal and unaffected, and the bulging is the result 

 of mechanical contraction and expansion by cold and heat. This 

 is possible only where the seal of the cans is not entirely her- 

 metical. In the case of the Gebee seal with the burr cap, and 

 the McDonald seal with the friction cap, the seal is not absolutely 

 air-tight. While the pores between cap and can are microscopic 

 in size, and not large enough to permit the contents from leak- 

 ing out, they are sufficient to admit air. The cans are usually 

 filled with the condensed milk at a temperature of about 70 de- 

 grees F. If the filled and sealed cans are exposed to a very 

 low temperature, as may be the case in winter, in store houses or 

 in transit, the milk and the air in the cans contract. This con- 

 traction is intensified by the fact that the sweetened condensed 

 milk does not freeze. Its concentration is so great that its freez- 

 ing point is usually below the most extreme cold storage tem- 



1 Hunziker, Results not published. 



